This invention relates to acoustic surface wave devices and in particular to such devices which have reduced temperature coefficient of propagation delay.
U.S. Pat. No. 3,818,382 (Holland et al.) discloses a surface wave device having reduced temperature coefficient of propagation delay. Holland's device uses the principle that X-propagating rotated Y-cut quartz has a zero temperature coefficient of propagation delay at a temperature which may be selected in accordance with the cut angle of the quartz substrate. In particular Holland points out that X-propagating rotated Y-cut quartz has a zero coefficient of propagation delay at 50.degree. C when the cut angle of the crystal is 39-1/2.degree. and has a zero temperature coefficient of propagation delay at 0.degree. C when the crystal has a cut angle of 46-1/2.degree. . As indicated in the FIG. 1 diagram of the Holland specification, a rotation of the cut angle of the crystal away from the Y-axis causes a reduction in the piezoelectric coupling coefficient as well as a reduction in the temperature at which the zero temperature coefficient point occurs.